Improved variational methods in statistical data assimilation
Summary: We propose an improved method of data assimilation, in which measured data are incorporated into a physically based model. In data assimilation, one typically seeks to minimize some cost function; here, we discuss a variational approximation in which model and measurement errors are Gaussian, combined with an annealing method, to consistently identify a global minimum of this cost function. We illustrate this procedure with archetypal chaotic systems, and discuss higher-order corrections.
Nonlin. Processes Geophys., 22, 205-213, doi:10.5194/npg-22-205-2015, 2015
Analysis of stochastic model for nonlinear volcanic dynamics
Summary: We consider a dynamic model of the magma-plug system previously derived by Iverson R. M. et al. (2006, Nature, 444) under the influence of stochastic forcing. The effects of noise-induced shifts, pressure stabilization and localization of random trajectories have been revealed by increasing the noise intensity. It is demonstrated that the repetitive stick-slip motions of the magma-plug system in the case of stochastic forcing can be connected with drumbeat earthquakes.
Nonlin. Processes Geophys., 22, 197-204, doi:10.5194/npg-22-197-2015, 2015
Statistical optimization for passive scalar transport: maximum entropy production versus maximum Kolmogorov–Sinai entropy
Nonlin. Processes Geophys., 22, 187-196, doi:10.5194/npg-22-187-2015, 2015
Equilibrium temperature distribution and Hadley circulation in an axisymmetric model
Summary: At the Equator, where the heating is larger than that at other latitudes, air rises and diverges poleward in the upper troposphere, descending more or less at 30° latitude; this circulation is the Hadley cell. We studied the impact of different meridional and vertical temperature distributions on a few features of the Hadley cell. Some parameters show a regular dependence on these distributions; others remain rather stable with distributions, but when they change, they do it in an abrupt way.
Nonlin. Processes Geophys., 22, 173-185, doi:10.5194/npg-22-173-2015, 2015
Brief Communication: The double layer in the separatrix region during magnetic reconnection
Summary: The key finding is that an electron beam can be generated in the separatrix region as magnetic reconnection proceeds. This electron beam could trigger the ion-acoustic instability, and a double layer accompanied with electron holes can be found during the nonlinear evolution stage of this instability.
Nonlin. Processes Geophys., 22, 167-171, doi:10.5194/npg-22-167-2015, 2015
Evaluation of empirical mode decomposition for quantifying multi-decadal variations and acceleration in sea level records
Summary: The ability of empirical mode decomposition (EMD) to extract multi-decadal variability from sea level records is tested using three simulations, based on sinusoidal oscillations and climate indices. In all cases, the longest-period modes are significantly distorted, with incorrect amplitudes and phases. This affects the estimated acceleration computed from the longest periodic IMF. Additionally, in all cases, extra low-frequency modes uncorrelated with the prescribed variability are found.
Nonlin. Processes Geophys., 22, 157-166, doi:10.5194/npg-22-157-2015, 2015
Geometric and topological approaches to significance testing in wavelet analysis
Nonlin. Processes Geophys., 22, 139-156, doi:10.5194/npg-22-139-2015, 2015
Time-dependent Long's equation
Summary: Long's equation models the steady state of two-dimensional stratified flow over terrain. It has been used extensively to investigate the generation and properties of gravity waves and their impact on the structure constants of the atmosphere. In this paper we derive a time-dependent version of this equation which might be useful in the analysis of experimental data about gravity waves.
Nonlin. Processes Geophys., 22, 133-138, doi:10.5194/npg-22-133-2015, 2015
Propagation regimes of interfacial solitary waves in a three-layer fluid
Summary: We have derived exact analytical expressions for the coefficients of evolution equations of long wave motion in the three-layer fluid with arbitrary parameters of the layers and established interrelations of these equations for different interfaces. To our understanding, the core advancement is the clarification and mapping of the regimes of soliton appearance and propagation in this environment that is much more realistic for the description of ocean internal waves.
Nonlin. Processes Geophys., 22, 117-132, doi:10.5194/npg-22-117-2015, 2015
Estimation of flow velocity for a debris flow via the two-phase fluid model
Nonlin. Processes Geophys., 22, 109-116, doi:10.5194/npg-22-109-2015, 2015
Non-Gaussian interaction information: estimation, optimization and diagnostic application of triadic wave resonance
Summary: Non-Gaussian joint PDFs and Shannon negentropies allow for nonlinear correlations and synergetic interaction information among random variables. Third-order cross-cumulants (triadic correlations -- TCs) under pair-wise (total or partial) independence are maximized on projections and orthogonal rotations of the full PDF. Fourier analysis allows decomposing TCs as wave resonant triads working as non-Gaussian sources of dynamical predictability. An illustration is given in a minimal fluid model.
Nonlin. Processes Geophys., 22, 87-108, doi:10.5194/npg-22-87-2015, 2015
Fluctuations in a quasi-stationary shallow cumulus cloud ensemble
Nonlin. Processes Geophys., 22, 65-85, doi:10.5194/npg-22-65-2015, 2015
Site effect classification based on microtremor data analysis using a concentration–area fractal model
Nonlin. Processes Geophys., 22, 53-63, doi:10.5194/npg-22-53-2015, 2015
Inferring origin of mercury inclusions in quartz by multifractal analysis
Summary: In order to refine our understanding of how fluid inclusions were trapped in the host minerals, we observed mercury inclusions in quartz samples using X-ray computed tomography technique. We obtained three-dimensional spatial distributions, and analyzed them using fractal and multifractal methods. Given the fractal dimension and its implied mechanism, the mercury-bearing fluids were not primary fluid inclusions, but migrated into the pre-existing cracks of quartz crystals by diffusion processes.
Nonlin. Processes Geophys., 22, 47-52, doi:10.5194/npg-22-47-2015, 2015
On the data-driven inference of modulatory networks in climate science: an application to West African rainfall
Summary: We applied coupled heterogeneous association rule mining (CHARM), Lasso multivariate regression, and dynamic Bayesian networks to find relationships within a complex system, and explored means with which to obtain a consensus result from the application of such varied methodologies. Using this fusion of approaches, we identified relationships among climate factors that fall into two categories: well-known associations from prior knowledge, and putative links that invite further research.
Nonlin. Processes Geophys., 22, 33-46, doi:10.5194/npg-22-33-2015, 2015
Toward the assimilation of images
Nonlin. Processes Geophys., 22, 15-32, doi:10.5194/npg-22-15-2015, 2015
Multiple-scale error growth in a convection-resolving model
Nonlin. Processes Geophys., 22, 1-13, doi:10.5194/npg-22-1-2015, 2015
Dependence of sandpile avalanche frequency–size distribution on coverage extent and compactness of embedded toppling threshold heterogeneity: implications for the variation of Gutenberg–Richter b value
Nonlin. Processes Geophys., 21, 1185-1193, doi:10.5194/npg-21-1185-2014, 2014
Large eddy simulation of sediment transport over rippled beds
Nonlin. Processes Geophys., 21, 1169-1184, doi:10.5194/npg-21-1169-2014, 2014
An improved ARIMA model for precipitation simulations
Summary: This paper presents an improvement on the conventional ARIMA model for precipitation time-series forecast. The precipitation time series of 12 months is first classified into several clusters. The maxima, minima, and truncation means of each cluster are then predicted using the improved ARIMA models, which are further used to predict the monthly precipitation through a set of regression models. A case study demonstrates that the present approach could increase the forecast accuracy by 21%.
Nonlin. Processes Geophys., 21, 1159-1168, doi:10.5194/npg-21-1159-2014, 2014